An electrical system, such as a computer, for example, may include components mounted on printed circuit boards, such as daughter cards, backplane boards, motherboards, and the like, that are interconnected to transfer power and data signals throughout the system.
Typically, a printed circuit board is a combination of stacked ground, trace, and dielectric layers. The ground layers and the trace layers in such printed circuit boards extend to peripheral edges of the board. In some circumstances a right angle electrical connector may be configured to mount onto the printed circuit board such that a portion of the connector overhangs an edge of the printed circuit board. The right-angle electrical connector includes a connector housing that supports a plurality of electrical signal contacts and electrical ground contacts disposed between adjacent electrical signal contacts. As a result of the overhang, signal degrading crosstalk may occur in the ground layers (in particular the first ground layer) of the printed circuit board.
For example, as shown in FIGS. 1A and 1B, a conventional electrical connector assembly 8 includes a right-angle electrical connector 10 mounted onto a printed circuit board or substrate 14. The electrical connector 10 includes a dielectric connector housing that supports a plurality of electrical contacts 56, including signal contacts 57 and ground contacts 59. The electrical contacts 56, including the signal contacts 57, can each define a mating portion 68, a mounting portion 70, a first transition portion 72 connected to the mating portion 68, and a second transition portion 74 connected between the first transition portion 72 and the mounting portion 70. The signal contacts 57 are configured to transmit data signals between the substrate 14 and a complementary electrical component that is mated to the electrical connector 10.
As shown, the substrate 14 may include at least one, such as a plurality of trace layers 22, at least one, such as a plurality of ground layers 26, and at least one, such a plurality of dielectric layers 30 disposed between the trace layers 22 and the ground layers 26. The trace layer 22 is illustrated schematically as a continuous layer, though it should be appreciated that the trace layer 22 includes individual traces that are configured to selectively electrically connect to individual ones of the electrical signal contacts 57 of the electrical connector 10, adjacent ones of which can define differential signal pair such that the electrical ground contacts 59 are disposed between adjacent differential signal pairs.
For instance, the substrate 14 can define a first plurality of signal vias 45 that are electrically connected to the trace layers 22 and ground vias 47 that are electrically connected to the ground layers 26. Thus, when the mounting portion 70 of the signal contacts 57 are inserted into respective ones of the signal vias 45, the signal contacts 57 are electrically connected to respective traces of the substrate 14. Likewise, when the mounting portion 70 of the ground contacts 59 are inserted into respective ones of the ground vias 47, the ground contacts 59 are electrically connected to the ground layers 26 of the substrate 14. The ground vias 47 are electrically isolated from the trace layers 22, and the signal vias 45 are electrically isolated from the ground layers 26.
As shown, the trace layers 22 each include a trace layer edge 40 that is flush with a first ground layer edge 44 of each ground layer 26. The trace layer edges 40 and the ground layer edges can partially define a substrate edge 48. During operation of the electrical connector 10, at least a portion of the electromagnetic fields generated by the electrical signal contacts 57 are communicated to the upper ground layers 26, resulting in noise that is carried by the upper ground layers 26. As shown in FIGS. 1A and 1B, when the electrical connector 10 is mounted onto the substrate 14, a portion 52 of the connector 10 overhangs and abuts the substrate edge 48. Typically, the first transition portion 72 of at least the lowermost signal contact S1 crosses the first ground edge 44 of the ground layer 26, and the second transition portion 74 is positioned adjacent an upper surface of the ground layer 26 and overlaps the ground layer 26 by a common length CL when the electrical connector 10 is mounted on the substrate 14. Because the first transition portion 72 and the second transition portion 74 of the lowermost signal contact S1 is disposed proximate to the noise-carrying ground layers 26 of the substrate 14, crosstalk can be generated on at least the lowermost signal contact S1 that tends to degrade the signal carried by the lowermost signal contact S1.